Aircraft, particularly in the field of transport aircraft, generally make use of aerodynamic control airfoils distributed over the aerodynamic surfaces to control motions around the center of gravity of the aircraft: wings or fins, on the fuselage.
The aerodynamic airfoils are most often dedicated to a function due to their principal effects on the aircraft: ailerons to control torque around the roll axis, elevators to control torque around the pitch axis, directional airfoils to control torque around the yaw axis, aerodynamic brakes to control aerodynamic drag, and lift destroyers or “spoilers” to control the aerodynamic lift of the wing.
To combine the effects of an attitude control airfoil: aileron, depth or directional control airfoil, with those of aerodynamic brakes, it is known how to utilize airfoils called crocodile airfoils.
The crocodile airfoils placed at the ends of the wing can also serve to create yaw torques in particular for control around the yaw axis on aircraft that do not have yaw fins or that have no rudder. The use of crocodile airfoils as aerodynamic brakes in these cases is a consequence of the possibilities offered by these airfoils.
For example U.S. Pat. No. 1,974,407 shows the case of a crocodile airfoil that has two movable surfaces hinged to the same shaft integral with a rear spar of the wing, forming a top face of the airfoil and with the other forming a bottom face of the airfoil.
The two movable surfaces of such an airfoil when they are joined together and turned simultaneously while remaining joined behave like a conventional airfoil such as an aileron or a directional airfoil in having a similar overall geometry.
When the two movable surfaces are set at different angles apart from one another, they are in different orientations with respect to the aerodynamic flow and also behave like an aerodynamic brake.
The Patent Application GB 722842 or Application WO 2007/068450 show another embodiment of a crocodile airfoil in which the two movable surfaces forming the airfoil are hinged individually, to be more or less removed symmetrically relative to a central plane, to a forward section itself hinged to the aircraft structure, to be turned in unison.
The advantage of such crocodile airfoils accordingly is to be able to accomplish the two airfoil functions on the one hand by simultaneously setting the movable surfaces constituting the airfoil, and on the other hand by differential aerodynamic braking of these movable surfaces, with the ability to combine the two modes.
Such crocodile airfoils, however, are still seldom used, principally because of installation problems posed by the proposed embodiments.
The airfoils such as ailerons, elevation or directional airfoils, are hinged on the side of the trailing edge of the load-bearing aerodynamic surface with which they are associated, such as a wing, a horizontal or vertical fin, in other words in a zone of reduced thickness.
The installation of two movable surfaces to be hinged for being set individually in this reduced thickness involves difficulties in structural design of the movable surfaces, and especially of their hinges and the absorption of forces on the rear spar of the load-bearing aerodynamic surface, and on the installation of the drivers necessary to provide for setting the two movable surface, everything being done with aerodynamic sacrifices as small as possible.
These installation difficulties lead to complex and heavy assemblies that introduce limitations into the settings of the two movable surfaces of the crocodile airfoil, and do not permit deriving any benefit that can be expected from a crocodile airfoil.
Also, the different hinges and the motions associated with these installation conditions lead to maintaining the functional play of parasitic aerodynamic drag and act to disfavor the aerodynamic balance of the crocodile airfoils.